1. Field of the Invention
The present invention relates to a method for producing ceramics having a small coefficient of thermal expansion and improved thermal shock resistance. More particularly, it relates to a method for producing ceramics having good thermal shock resistance suitable for use in making a catalyst carrier, a combustion apparatus and the like.
2. Description of the Prior Arts
Conventional ceramics having a small coefficient of thermal expansion and good thermal shock resistance include cordierite ceramics, lithia type ceramics, aluminum titanate ceramics and the like. The cordierite ceramics are MgO--Al.sub.2 O.sub.3 --SiO.sub.2 type one. The lithia type ceramics is a Li.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 type. The cordierite type ceramics are prepared by mixing talc [Mg.sub.3 (Si.sub.4 O.sub.10)(OH).sub.2 ], kaolin [Al.sub.2 Si.sub.2 O.sub.5 (OH).sub.4 ] and alumina (Al.sub.2 O.sub.3) in an adequate ratio, followed by dehydration, molding, drying and calcining. For example, calcination of the mixture is carried out at about 1,400.degree. C. for 4 to 5 days (cf. Japanese Patent Publication Nos. 1564/1979 and 20358/1976). The aluminum titanate ceramics is prepared by calcining a mixture of titanium oxide (anatase type) and highly pure .alpha.-alumina in an equimolar amount at 1,600.degree. C. to 1,700.degree. C. (cf. "Yogyokogaku Handbook" (Ceramic Industry Handbook), p 1274, Gihodo, Japan).
However, the conventional thermal shock resistant ceramics have sufficient mechanical strength only when they are calcined at a high temperature for a long period of time. In addition, the synthesized ceramics may not be dense or may tend to be cracked at particle boundaries. Therefore, they lack dimensional accuracy and their thermal shock resistance is not satisfactory.